1. Field of the Invention
This invention relates to pneumatic radial tires and more particularly to such tires having belt plies reinforced with selected fibrous and metallic materials.
2. Description of the Prior Art
Aromatic polyamide fibers, typified by "Kevlar" fibers of E. I. DuPont Nemours & Co., Inc., are known to be by far mechanically strong and highly elastic than fiber-reinforced tire cords in common use. Such polyamide fibers hereunder referred to as "aramid fibers" have enjoyed a commercial credit as lending themselves to high-quality automobile tires. Many approaches have been proposed with the aramid fibers in the art.
The aramid fibers, however, are difficult to fully exhibit their superior physical characteristics as tire reinforcements because they are not sufficiently adhesive to rubber compared to commonly used fibrous tire cords. Due to their insufficient water-resistant adhesion, the aramid fibers when employed for a tire belt tend to invite objectionable ply separation upon moisturing. While a fiber-reinforced belt is preferred to be disposed adjacent to a tread portion, such aramid fibers have much to be desired to meet the tire reinforcing requirements.
In general, an aramid fiber cord is used in combination with a different cord formed for example of steel wires so as to attain improved reinforcement. Two coat rubbers of different compositions have been used to assemble both cords. One of the coat rubbers has adhesiveness to the aramid fibers and the other to the metallic wires. However, such prior mode of coating leaves the problem that the coat to coat difference in modulus and other physical qualities takes place, resulting in separated ply. This also gives rise to a decline in belt processability and often times tire quality.